Ultrasound ablation catheter and method for its use

ABSTRACT

Catheters and methods for epicardial ablation are provided. A suitable catheter comprises an elongated catheter body and an ultrasound transducer mounted at or near the distal end of the catheter body. The transducer has a front surface and an opposing back surface, wherein the transducer is positioned to transmit ultrasound energy toward tissue facing the front surface but not toward tissue facing the back surface. A sensor is mounted within the catheter near the ultrasound transducer for sensing a location and an orientation of the ultrasound transducer within a patient. A suitable method involves introducing the distal end of the catheter introducing into the pericardium of a patient. The transducer&#39;s front surface is positioned so that it generally faces tissue to be ablated, and the tissue is ablated with ultrasound energy generated by the transducer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No.10/621,988 filed Jul. 17, 2003, now U.S. Pat. No. 7,678,104, the entirecontents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Standard radio frequency (RF) ablation, performed using one or moreelectrode elements, is not very successful for epicardial ablationbecause it is not directional. RF ablation creates a lesion that burnsthe tissue in all directions, thereby burning the pericardium. As theburned pericardium heals, it tends to adhere to the epicardial tissue.Further, the lesions created using RF ablation are too shallow to beeffective. Thus, a need exists for a catheter that is particularlyeffective for epicardial ablation.

SUMMARY OF THE INVENTION

The invention is directed to catheters and methods for epicardialablation using ultrasound energy. In one embodiment, the invention isdirected to a catheter that is particularly useful for epicardialablation. The catheter comprises an elongated catheter body havingproximal and distal ends. An ultrasound transducer is mounted at or nearthe distal end of the catheter body. The transducer has a front surfaceand an opposing back surface. The transducer is positioned to transmitultrasound energy toward tissue facing the front surface but not towardtissue facing the back surface. A sensor is mounted within the catheterbody near the ultrasound transducer for sensing a location and anorientation of the ultrasound transducer within a patient. With thiscatheter, the operator can easily determine the precise location andorientation of the ultrasound transducer to assure that the ablationenergy is reaching the tissue to be treated.

In another embodiment, the invention is directed to a cathetercomprising an elongated catheter body having proximal and distal ends. Atip electrode is mounted at the distal end of the catheter body. The tipelectrode has an exposed electrode surface and a transducer mountingsurface opposite the exposed electrode surface. An ultrasound transduceris mounted on the transducer mounting surface of the tip electrode.

In yet another embodiment, the invention is directed to a cathetercomprising an elongated catheter body having proximal and distal ends.An ultrasound transducer mounted at or near the distal end of thecatheter body. The transducer has a front surface and an opposing backsurface. The transducer is positioned to transmit ultrasound energytoward tissue facing the front surface but not toward tissue facing theback surface. A control handle is mounted at the proximal end of thecatheter body. A deflection wire extends through the catheter body. Thedeflection wire has a distal end fixedly attached near the catheterbody's distal end and a proximal end anchored to a mechanism in thecontrol handle that facilitates longitudinal movement of the deflectionwire relative to the catheter body. The deflection wire is anchored at aposition that is about 70° to 120° relative to the direction that energyis emitted from the transducer to thereby deflect the distal end of thecatheter in a direction generally transverse to the direction thatenergy is emitted from the transducer.

In still another embodiment, the invention is directed to a method forepicardial ablation in a patient. The method comprises introducing intothe pericardium of a patient a distal end of a catheter comprising anelongated tubular body with a transducer mounted at or near the distalend of the tubular body. The transducer has a front surface and anopposing back surface. The transducer is positioned to transmitultrasound energy toward tissue facing the front surface but not towardtissue facing the back surface. The transducer's front surface ispositioned so that it generally faces tissue to be ablated. The tissueto be ablated is then ablated with ultrasound energy generated by thetransducer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a side view of an embodiment of the catheter of the invention.

FIG. 2 is a side cross-sectional view of a catheter body according tothe invention, including the junction between the proximal shaft anddistal shaft.

FIG. 3 is a perspective view of a transducer mounted on a tip electrodeaccording to the invention.

FIG. 4 is a side view of a tip electrode according to the invention,with the holes and passages within the tip electrode shown in phantom.

FIG. 5 is an end cross-sectional view of the tip electrode of FIG. 4along line 5-5.

FIG. 6 is an end cross-sectional view of the tip electrode of FIG. 4along line 6-6.

FIG. 7 is an end cross-sectional view of a tip electrode of theinvention, including the cable, tube and wires extending into the tipelectrode.

FIG. 8 is a side cross-sectional view of the distal end of a catheteraccording to the invention showing that extend within the exposedsection of the tip electrode.

FIG. 9 is an enlarged view of the thermocouple wires mounted in the tipelectrode of FIG. 8.

FIG. 10 is an end cross-sectional view of the tubing of the distal shaftshown in FIG. 8 along line 10-10.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the catheter comprises an elongated catheter body 10including a proximal shaft 12 and a distal shaft 14 and a control handle16 at the proximal end of the proximal shaft.

With reference to FIG. 2, the proximal shaft 12 comprises an elongatedtubular construction having a single, axial or central lumen 18. Theproximal shaft 12 is flexible, i.e., bendable, but substantiallynon-compressible along its length. The proximal shaft 12 can be of anysuitable construction and made of any suitable material. A presentlypreferred construction comprises an outer wall 22 made of a polyurethaneor nylon. The outer wall 22 comprises an imbedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter body 10 so that, when the control handle 16 is rotated, thedistal shaft 14 will rotate in a corresponding manner.

The outer diameter of the proximal shaft 12 is not critical, but ispreferably no more than about 8 french, more preferably no greater thanabout 7 french. Likewise the thickness of the outer wall 22 is notcritical. If desired, the inner surface of the outer wall 22 may belined with a stiffening tube (not tube), which, along with the braidedouter wall 22, can provide improved torsional stability while at thesame time minimizing the wall thickness of the catheter, thus maximizingthe diameter of the central lumen 18. An catheter including a stiffeningtube is described in more detail in U.S. Pat. No. 6,203,507, thedisclosure of which is incorporated herein by reference.

In the depicted embodiment, the distal shaft 14 comprises a shortsection of flexible tubing 19 having three lumens, a puller wire lumen30, an irrigation lumen 32, and a cable and wire lumen 34. The tubing 19is made of a suitable non-toxic material that is preferably moreflexible than the proximal shaft 12. A presently preferred material forthe tubing 19 is braided polyurethane, i.e., polyurethane with anembedded mesh of braided stainless steel or the like, that is moreflexible than the catheter body. The number and size of the lumens isnot critical and can vary depending on the various wires, tubes andother components carried by the catheter. In a preferred embodiment, thedistal shaft 14 has an outer diameter ranging from about 5 french (0.066inch) to 8 french (0.105 inch).

One means for attaching the proximal shaft 12 to the distal shaft 14 isillustrated in FIG. 2. The proximal end of the distal shaft 14 comprisesan outer circumferential notch 24 that receives the inner surface of theouter wall 22 of the proximal shaft 12. The distal shaft 14 and proximalshaft 12 are attached by glue or the like. Other arrangements forjoining the proximal and distal shafts are considered within the scopeof the invention. For example, the proximal and distal shafts can bemade from a single tubing so that the proximal and distal shafts includethe same number of lumens. Alternatively, if a stiffening tube isprovided, the stiffening tube can extend slightly beyond the distal endof the proximal shaft 12 (e.g., about 3 mm) and be glued to the proximalshaft, with the proximal end of the distal shaft 14 cored out to receivethe distal end of the stiffening tube, creating a lap joint. The lapjoint and the butt joint formed between the distal end of the proximalshaft 12 and the proximal end of the distal shaft 14 can be secured withpolyurethane glue or the like. In another alternative, the proximalshaft 12 can be thermally fused to the distal shaft 14.

If desired, a spacer (not shown) can be located within the proximalshaft 12 at its distal end, adjacent the proximal end of the distalshaft 14. The spacer provides a transition in flexibility at thejunction of the proximal shaft and distal shaft, which allows thisjunction to bend smoothly without folding or kinking. A catheter havingsuch a spacer is described in U.S. Pat. No. 5,964,757, the disclosure ofwhich is incorporated herein by reference.

At the distal end of the distal shaft 14 is a tip electrode 36. As shownin FIGS. 3 and 4, the tip electrode 36 has an exposed section 37 havinga length ranging preferably from about 2 mm to about 10 mm, morepreferably from about 6 mm to about 8 mm, and a stem 39 having adiameter less than the diameter of the exposed section and having alength ranging preferably from about 1 mm to about 6 mm, more preferablyfrom about 2 mm to about 4 mm.

The exposed section 37 of the tip electrode 36 includes an ultrasoundtransducer 38 mounted thereon. In the depicted embodiment, the exposedsection 37 of the tip electrode 36 has an outer ablation surface 40 thatis generally co-linear with the outer surface of the tubing 19 andgenerally rounded like the outer surface of the tubing. The exposedsection 37 also includes a cut-out region to provide a transducersurface 42 on which the transducer 38 is mounted. Preferably the cut-outregion is sufficiently deep so that, when the transducer 38 is mountedon the transducer surface 42, the transducer does not extend beyond theouter circumference of the tubing 19.

In the depicted embodiment, the transducer 38 comprises threegenerally-rectangular and generally-flat layers. The central layer 44 isa generally rectangular plate comprising a piezoceramic or piezoelectriccrystalline material. The central layer 44 preferably is made of a typePZT-4, PZT-5 or PZT-8, quartz or Lithium-Niobate type piezoceramicmaterial to ensure high power output capabilities. These types oftransducer materials are commercially available from Stavely Sensors,Inc. (East Hartford, Conn.) and from Valpey-Fischer Corp. (Hopkinton,Mass.). The outer and inner layers 43 and 45 enclose the central layer44 and are each constructed of an electrically conductive material,thereby forming transducer electrodes. These outer and inner transducerlayers 43 and 45 may each comprise a metallic coating, such as a coatingof nickel, copper, silver, gold, platinum, or an alloy thereof. Theinner transducer layer 45 can be mounted onto the tip electrode 36 inany suitable manner, for example, by soldering the inner transducerlayer to the transducer surface 42 of the tip electrode.

The length of the transducer 38 is selected for a given clinicalapplication and is desirably not longer than the length of the exposedsection 37 of the tip electrode 36. The transducer 38 length preferablyranges from about 2 mm to about 10 mm, more preferably from about 5 mmto about 10 mm. The central layer 44 of the transducer 38 has athickness selected to produce a desired operating frequency. Theoperating frequency will vary depending upon clinical needs, such as thedepth of heating, as well as upon the size of the transducer as limitedby the delivery path and the size of the target site. The transducer 38in the illustrated embodiment preferably operates at a frequency rangingfrom about 5 MHz to about 20 MHz, and more preferably from about 7 MHzto about 10 MHz. Thus, for example, the transducer can have a thicknessof approximately 0.3 mm for an operating frequency of about 7 MHz (i.e.,a thickness generally equal to ½ the wavelength associated with thedesired operating frequency).

The piezoelectric crystal that forms the central layer 44 of theultrasound transducer 38 is adapted to contract and expand (or“vibrate”) when an alternating current is applied from a current sourceand across the outer and inner layers 43 and 45. This controlledvibration emits the ultrasonic energy direction away from and generallyperpendicular to the generally flat surfaces of the outer and innerlayers 43 and 45 to thereby ablate tissue. However, because the innerlayer 45 is facing the transducer surface 42 of the tip electrode 36,the energy emitted from the inner layer 45 does not ablate tissue. As aresult, ablation can be controlled by directing the ultrasound energy inone direction, i.e., away from the flat surface of the outer layer 43.

The transducer 38 preferably is “air-backed” to produce more energy andto enhance energy distribution uniformity, as is known in the art. Inother words, the inner transducer layer 45 does not contact anappreciable amount of the transducer surface 42 of the tip electrode 36.As best shown in FIGS. 5 and 6, the transducer surface 42 of the tipelectrode 36 is slightly concave, and the inner transducer layer 45 isgenerally flat. The bottom edges 46 of the inner transducer layer 45 aresoldered to the transducer surface 42, thereby leaving an air-gapbetween the central region of the inner transducer layer and thetransducer surface. The sides and the proximal and distal ends of thetransducer 38 are then sealed, for example, with epoxy or a siliconeglue (not shown), which is a good sealant and resistant to hightemperatures. When the sides and the ends of the transducer 38 aresealed, air is trapped in the air-gap between the transducer and thetransducer surface 42 of the tip electrode 36. The air in the air-gapreflects the ultrasound energy directed toward the tip electrode 36 sothat the ultrasound energy reverses direction, providing more energy inthe desired direction, i.e., toward the tissue to be ablated.

For applying an alternating current from a current source across theouter and inner layers 43 and 45, electrical transducer leads areelectrically coupled to outer and inner layers of the transducer 38 byany suitable method. In the depicted embodiment, a coaxial cable 48 isprovided, which includes a coaxial center and a coaxial shield. Thecoaxial center is connected to the outer transducer layer 43 with acoaxial center wire 51 by solder or the like. The coaxial shield 52 isconnected to the inner transducer layer 45 by soldering a coaxial shieldwire 53 to the coaxial shield and to the tip electrode 36, which, asnoted above, is attached to the inner transducer layer. The proximalends of the coaxial center and coaxial shield of the coaxial cable 48are adapted to couple to an appropriate ultrasound or radiofrequencygenerator (not shown).

The coaxial cable 48 extends through the central lumen 18 of theproximal shaft 12 and through the cable and wire lumen 34 of the distalshaft 14. The coaxial center wire 51 extends through a wire passage 54in the tip electrode 36. As best shown in FIG. 4, the wire passage 54,which extends through the stem 39 and a part of the exposed section 37of the tip electrode, is on the side of the tip electrode including thecut-out, i.e., the side on which the transducer 38 is mounted. Thecoaxial shield wire 53 that connects the coaxial shield to the tipelectrode 36 extends into a first blind hole 56 in the tip electrode andis soldered within the first blind hole. Other arrangements for thetransducer wires are within the scope of the invention.

A radiofrequency (RF) generator (not shown) introduces electricalcurrent to the transducer 36, which converts the electrical current intoultrasonic pressure waves. Alternatively, An ultrasonic generator can beused to generate alternating current to power the transducer 36. Theultrasonic generator drives the transducer at frequencies ranging fromabout 5 to about 20 MHz, and preferably for the illustrated applicationranging from about 7 MHz to about 10 MHz. In addition, the ultrasonicgenerator can modulate the driving frequencies and/or vary power tosmooth or unify the produced collimated ultrasonic beam. For instance,the function generator of the ultrasonic generator can drive thetransducer at frequencies ranging from about 6.8 MHz to about 7.2 MHz bycontinuously or discretely sweeping between these frequencies.

With this design, the transducer 38 has a front surface, i.e., thesurface of the outer layer 43 farthest from the transducer surface 42 ofthe tip electrode 36, and an opposing back surface, i.e., the surface ofthe inner layer 45 nearest the transducer surface of the tip electrode.The tip electrode 36 prevents the transducer 38 from transmittingultrasound energy toward tissue facing the back surface, so that thetransducer is positioned to transmit ultrasound energy toward only thetissue facing the front surface. The transducer 38 is preferablygenerally flat, as depicted in FIG. 3, but could be slightly curved ifdesired. If desired, the transducer 38 can be mounted on the distalshaft 14 instead of on the tip electrode 36.

The tip electrode 36 is connected to the distal shaft tubing 19 by meansof a generally rigid tubular plastic housing 21, preferably made ofpolyether-etherketone (PEEK). The stem 39 of the tip electrode 36 fitsinside the distal end of the plastic housing 21 and is bonded to thehousing by polyurethane glue or the like. The proximal end of theplastic housing 21 is bonded with polyurethane glue or the like to thedistal end of the tubing 19 of the distal shaft 14. It is understoodthat the tip electrode alternatively may be connected directly to thetubing 19 of the distal shaft 14 as desired as is well known in the art.If desired, the transducer 38 can be mounted on the plastic housing 21instead of on the tip electrode 36.

In the embodiment shown, a ring electrode 58 is mounted on the distalend of the plastic housing 21. The ring electrode 58 is slid over theplastic housing 21 and fixed in place by glue or the like. If desired,additional ring electrodes may be used and can be positioned over theplastic housing 21 or over the flexible tubing 19 of the distal shaft14.

The tip electrode 36 and ring electrode 58 are each connected to aseparate lead wire 60. The lead wires 60 extend through the plastichousing 21, the cable and wire lumen 34 of the distal shaft 14, thecentral lumen 18 of the proximal shaft 12, and the control handle 16,and each terminates at its proximal end in an input jack 29 that may beplugged into an appropriate monitor (not shown) and/or source of radiofrequency or other ablation energy (not shown). If desired, the portionof the lead wires 60 extending through the proximal shaft 12 and controlhandle 16 may be enclosed or bundled within a protective tube 26.

The lead wire 60 for the tip electrode 36 is anchored in the first blindhole 56 of the tip electrode by solder or the like. Any other means forelectrically-connecting the lead wire 60 to the tip electrode 36 mayalso be used.

A lead wire 60 is attached to the ring electrode 58 by any conventionaltechnique. Connection of a lead wire 60 to the ring electrode 58 ispreferably accomplished by first making a small hole through the plastichousing 21. Such a hole can be created, for example, by inserting aneedle through the plastic housing 21 and heating the needlesufficiently to form a permanent hole. A lead wire 60 is then drawnthrough the hole by using a microhook or the like. The ends of the leadwire 60 are then stripped of any coating and soldered or welded to theunderside of the ring electrode 58, which is then slid into positionover the hole and fixed in place with polyurethane glue or the like.

A temperature sensor is provided for the tip electrode 36 and, ifdesired, the ring electrode 58. Any conventional temperature sensor,e.g., a thermocouple or thermistor, may be used. A preferred temperaturesensor for the tip electrode 36 comprises a thermocouple formed by anenameled wire pair. One wire of the wire pair is a copper wire 62, e.g.,a number 40 copper wire. The other wire of the wire pair is a constantanwire 64. The wires 62 and 64 of the wire pair are electrically isolatedfrom each other except at their distal ends where they are twistedtogether, covered with a short piece of plastic tubing 66, e.g.,polyimide, and covered with epoxy. The plastic tubing 66 is then mountedin a second blind hole 57 in the tip electrode 36, and held in place bypolyurethane glue or the like. Alternatively, the wires 62 and 64 can besoldered into the second blind hole 57. In another alternativeembodiment, the copper wire 62 of the thermocouple can also be used as alead wire for the tip electrode 36.

The thermocouple wires 62 and 64 extend through the cable and wire lumen34 in the distal shaft 14 and through the central lumen 18 of theproximal shaft 12. The wires 62 and 64 then extend out through thecontrol handle 16 and to a connector (not shown) connectable to atemperature monitor (not shown).

An infusion tube 28 is provided for introducing fluid, such as saline,to the tip electrode 36. The infusion tube 28 is preferably made of abiocompatible plastic, such as polyimide. The infusion tube 28 has adistal end anchored in an irrigation passage 65 in the tip electrode 36.In the depicted embodiment, the irrigation passage 65 extends throughthe stem 39 and into exposed section 37 generally parallel to the axisof the tip electrode 36, but does not extend out the distal end of thetip electrode. Three irrigation branches 67 extend radially from theirrigation passage 65, as best shown in FIG. 6. Irrigation or coolingfluid can be introduced from the infusion tube 28 into the irrigationpassage 65 so that the fluid can pass out of the tip electrode 36through the irrigation branches 67 to thereby cool and/or irrigate theregion being ablated.

The infusion tube 28 extends through the irrigation lumen 32 of thedistal shaft 14, through the proximal shaft 12, out the proximal end ofthe control handle 16, and terminates in a luer hub 49 or the like at alocation proximal to the control handle. In an alternative arrangement,a single lumen side arm (not shown) is fluidly connected to the centrallumen 18 near the proximal end of the catheter body 10, as described inmore detail in U.S. Pat. No. 6,120,476, the entire disclosure of whichis incorporated herein by reference. Alternatively, the infusion tube 28can terminate within the distal end of the irrigation lumen 32 of thedistal shaft 14, with a second infusion tube (not shown) extending fromthe proximal end of the infusion lumen, through the proximal shaft 12and out through the control handle 16. Such a design is also describedin more detail in U.S. Pat. No. 6,120,476.

A puller wire 68 (or deflection wire) is provided within the catheterfor deflecting the distal shaft 14. The puller wire 68 is anchored atits proximal end to the control handle 16 and anchored at its distal endto the distal shaft 14. The puller wire 68 is made of any suitablemetal, such as stainless steel or Nitinol, and is preferably coated withTeflon® or the like. The coating imparts lubricity to the puller wire68. The puller wire 68 preferably has a diameter ranging from about0.006 to about 0.010 inches.

A compression coil 70 is situated with the proximal shaft 12 insurrounding relation to the puller wire 68. The compression coil 70extends from the proximal end of the proximal shaft 12 to the proximalend of the distal shaft 14. The compression coil 70 is made of anysuitable metal, preferably stainless steel. The compression coil 70 istightly wound on itself to provide flexibility, i.e., bending, but toresist compression. The inner diameter of the compression coil 70 ispreferably slightly larger than the diameter of the puller wire 68. Forexample, when the puller wire 68 has a diameter of about 0.007 inches,the compression coil 70 preferably has an inner diameter of about 0.008inches. The Teflon® coating on the puller wire 68 allows it to slidefreely within the compression coil 70. Along its length, the outersurface of the compression coil 70 is covered by a flexible,non-conductive sheath 72 to prevent contact between the compression coil70 and the lead wires 60 within the proximal shaft 12. A non-conductivesheath 72 made of polyimide tubing is presently preferred.

The compression coil 70 is anchored at its proximal end to the proximalend of the proximal shaft 12 by proximal glue joint 74 and at its distalend to the distal shaft 14 by distal glue joint 76. Both glue joints 74and 76 preferably comprise polyurethane glue or the like. The pullerwire 68 extends into the puller wire lumen 30 of the distal shaft 14.The puller wire 68 is anchored in the first blind hole 56 of the tipelectrode 36. In the depicted embodiment, the puller wire lumen 30 andthe first blind hole 56 are arranged at an angle of about 70° to about120°, more preferably about 90°, relative to the direction that energyis emitted from the transducer 38 to thereby deflect the distal end ofthe catheter in a direction generally transverse to, and preferablygenerally perpendicular to, the direction that energy is emitted fromthe transducer.

Preferably, a ferrule 69, made of stainless steel or the like, iscrimped onto the distal end of the puller wire 68 to add thickness tothe puller wire. The ferrule 69 is then attached to the inside of thefirst blind hole 56 of the tip electrode 36 with solder or the like.Alternatively, the puller wire 68 can be anchored to the side of thedistal shaft 14, as described in U.S. Pat. No. 6,571,131, the disclosureof which is incorporated herein by reference. Within the distal shaft14, the puller wire 68 extends through into a plastic, preferablyTeflon®, sheath 81, which prevents the puller wire 42 from cutting intothe wall of the distal shaft 14 when the distal shaft is deflected.

A location sensor 82 is contained within the distal end of the distalshaft 14 for sensing the position and orientation of the transducer 38.In the depicted embodiment, the location sensor 82 is mounted primarilywithin the plastic housing 21. The distal end of the location sensor 82extends into a trepanned region 84 in the proximal end of the stem 39 ofthe tip electrode 36. Depending on the length of the location sensor 82,its proximal end can extend into the tubing 19 of the distal shaft 14.The location sensor 82 is fixed in place by polyurethane glue or thelike. Alternatively, the location sensor 82 may be mounted proximal tothe tip electrode 36. Other arrangement for mounting the location sensor82 near the tip electrode 36 (and thus near the transducer 38) arewithin the scope of the invention. The location sensor 82 is mountedpreferably within 10 mm, more preferably within 5 mm, of the transducer38. In a particularly preferred embodiment, the location sensor 82 ispositioned directly under the transducer.

The location sensor 82 is connected to a sensor cable 84, which extendsthrough the cable and wire lumen 34 of the distal shaft 14, through theproximal shaft 12 and into the control handle 16. The sensor cable 84comprises multiple wires encased within a plastic covered sheath. Withinor outside the control handle 16, the sensor cable 84 is connected to acircuit board (not shown). The circuit board amplifies the signalreceived from the location sensor 82 and transmits it to a computer in aform understandable by the computer. Because the catheter is designedfor single use only, the circuit board may contain an EPROM chip thatshuts down the circuit board approximately 24 hours after the catheterhas been used. This prevents the catheter, or at least the locationsensor, from being used twice. A catheter having a control handle inwhich a circuit board is housed is described in U.S. Pat. No. [insert],the disclosure of which is incorporated herein by reference.

Preferably each location sensor 82 is an electromagnetic locationsensor. For example, each location sensor 82 may comprise amagnetic-field-responsive coil, as described in U.S. Pat. No. 5,391,199,or a plurality of such coils, as described in International PublicationWO 96/05758. The plurality of coils enables the six-dimensionalcoordinates (i.e. the three positional and the three orientationalcoordinates) of the location sensor 80 to be determined. Alternatively,any suitable location sensor known in the art may be used, such aselectrical, magnetic or acoustic sensors. Suitable location sensors foruse with the present invention are also described, for example, in U.S.Pat. Nos. 5,558,091, 5,443,489, 5,480,422, 5,546,951, and 5,568,809, andInternational Publication Nos. WO 95/02995, WO 97/24983, and WO98/29033, the disclosures of which are incorporated herein by reference.

Longitudinal movement of the puller wire 68 relative to the proximalshaft 12, which results in deflection of the distal shaft 14, isaccomplished by manipulation of the control handle 16. Examples ofsuitable control handles suitable for use in the present invention aredisclosed, for example, in U.S. Pat. Nos. Re 34,502 and 5,897,529, theentire disclosures of which are incorporated herein by reference.

If desired, two or more puller wires can be provided to enhance theability to manipulate the distal shaft. In such an embodiment, a secondpuller wire and a surrounding second compression coil extend through theproximal shaft and into an additional off-axis lumen in the distalshaft. If desired, the first puller wire can be anchored proximal to theanchor location of the second puller wire. Suitable designs of cathetershaving two or more puller wires, including suitable control handles forsuch embodiments, are described, for example, in U.S. Pat. Nos.6,123,699, 6,171,277, 6,183,435, 6,183,463, 6,198,974, 6,210,407, and6,267,746, the disclosures of which are incorporated herein byreference.

In use, the catheter is introduced into a patient so that the distal endof the catheter is positioned in or around a patient's heart. Thecatheter is particularly suitable for epicardial ablation. Withepicardial ablation, the distal end of the catheter is introduced intothe pericardium by any suitable technique. Examples of techniques thatcan be used in connection with the present invention include thosedisclosed in U.S. Pat. Nos. 6,161,543 and 6,314,963, the disclosures ofwhich are incorporated herein by reference. The distal end ismanipulated so that the transducer is generally facing the myocardialtissue. The directional nature of ultrasound energy, discussed above,makes it particularly suitable for ablating the myocardial tissuewithout also ablating the surrounding pericardial sack. Further, thedeep-penetrating nature of the ultrasound energy makes it particularlysuitable for burning deep lesions in the myocardial tissue.

Due to the directional nature of the ultrasound energy, it is highlydesirable to be able to view the relative positions of the transducer 38and the myocardial tissue to be ablated. The location sensor 82 permitsthis information to be easily determined. To use the location sensor 82,the patient is placed in a magnetic field generated, for example, byplacing a pad containing coils for generating a magnetic field under thepatient. A reference electromagnetic sensor is fixed relative to thepatient, e.g., taped to the patient's back, and the catheter containinga second electromagnetic sensor is advanced into the patient's heart.Each sensor comprises three small coils that, in the magnetic field,generate weak electrical signals indicative of their position in themagnetic field. Signals generated by both the fixed reference sensor andthe second sensor in the heart are amplified and transmitted to acomputer which analyzes the signals and then displays the signals on amonitor. By this method, the precise location of the sensor in thecatheter relative to the reference sensor can be ascertained andvisually displayed.

Using this technology, the physician can visually map the pericardium ora heart chamber. This mapping is done by advancing the catheter tip intoa heart chamber until contact is made with the heart wall. This positionand electrograms are recorded and saved. The catheter tip is then movedto another position in contact with the heart wall and again theposition is recorded and saved. This procedure is repeated until a threedimensional map of the heart chamber is achieved. The electromagneticmapping sensor 82 preferably is used in combination with the tipelectrode 36 and ring electrode 58. By combining the electromagneticsensor 82 and electrodes 36 and 58, a physician can simultaneously mapthe contours or shape of the heart chamber and the electrical activityof the heart.

After such a map is created, the physician can position the catheterwith the transducer 38 within the pericardium and use the locationsensor 82 to determine and adjust the position and orientation of thetransducer relative to the myocardial tissue to be ablated. Thetransducer 38 is then used to ablate a lesion in the myocardial tissue.The lesion preferably has a depth ranging from about 2 mm to about 5 mm.If desired, both the transducer 38 and tip electrode 36 can be used toablate tissue. In such an instance, ablation with the tip electrode 36can be performed before, during or after ablation with the transducer38.

Saline or other cooling or irrigation fluid can be passed through theirrigation branches 67 in the tip electrode 38 by introducing the fluidinto the infusion tube 28 through the luer hub 49. The use of coolingfluid to cool the tissue being ablated reduces or even eliminatesburning and charring of the tissue. For example, optimal burns having adepth of 2 to 3 mm were formed at 5 W/15 mL/min. Higher power was foundto result in tissue charring and a superficial burn, as the ultrasoundenergy probably does not penetrate through the char.

As noted above, the puller wire lumen 30 and the first blind hole 56 arearranged at an angle of about 90° relative to the direction that energyis emitted from the transducer 38. With this design, the transducer 38is mounted parallel to the deflection plane so that, when the catheteris in the pericardium, deflecting it would make the catheter sit flatwith the transducer pointing directly into the myocardium.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention.

Accordingly, the foregoing description should not be read as pertainingonly to the precise structures described and illustrated in theaccompanying drawings, but rather should be read consistent with and assupport to the following claims which are to have their fullest and fairscope.

1. A catheter comprising: an elongated catheter body having proximal anddistal ends, and a longitudinal axis; a tip electrode mounted at thedistal end of the catheter body, the tip electrode having an exposedelectrode surface and a transducer mounting surface, the transducermounting surface being positioned on an opposite side of thelongitudinal axis of the catheter body than the exposed electrodesurface, and wherein the tip electrode is fixed and non-rotationalrelative to the catheter body; and an ultrasound transducer mounted onthe transducer mounting surface of the tip electrode.
 2. The catheter ofclaim 1, wherein the transducer has a front surface and an opposing backsurface that faces the tip electrode, wherein the transducer ispositioned to transmit ultrasound energy toward tissue facing the frontsurface but not toward tissue facing the back surface.
 3. The catheterof claim 2, wherein the exposed surface of the tip electrode has alength ranging from about 2 mm to about 10 mm.
 4. The catheter of claim2, wherein the exposed surface of the tip electrode has a length rangingfrom about 6 mm to about 8 mm.
 5. The catheter of claim 1, wherein thetip electrode has an exposed surface and a stem having a diameter lessthan a diameter of the exposed surface, wherein the transducer ismounted on a surface of the exposed surface.
 6. The catheter of claim 1,further comprising a sensor mounted within the catheter body near theultrasound transducer for sensing a location and an orientation of theultrasound transducer within a patient.
 7. The catheter of claim 6,wherein the sensor is an electromagnetic location sensor.
 8. Thecatheter of claim 1, wherein the transducer is generally flat.
 9. Thecatheter of claim 1, wherein the transducer is generally rectangular.10. The catheter of claim 1, wherein the transducer has a length rangingfrom about 2 mm to about 10 mm.
 11. The catheter of claim 1, wherein thetransducer has a length ranging from about 5 mm to about 10 mm.
 12. Thecatheter of claim 1, further comprising means for deflecting the distalend of the catheter.
 13. The catheter of claim 12, wherein the means fordeflecting the distal end of the catheter comprises: a control handlemounted at the proximal end of the catheter body; and a deflection wireextending through the catheter body, the deflection wire having a distalend fixedly attached near the catheter body's distal end and a proximalend anchored to a mechanism in the control handle that facilitateslongitudinal movement of the deflection wire relative to the catheterbody.
 14. The catheter of claim 13, wherein the deflection wire isanchored at a position that is about 70° to 120° relative to thedirection that energy is emitted from the transducer to thereby deflectthe distal end of the catheter in a direction generally transverse tothe direction that energy is emitted from the transducer.
 15. Thecatheter of claim 13, wherein the deflection wire is anchored at aposition that is about 90° relative to the direction that energy isemitted from the transducer to thereby deflect the distal end of thecatheter in a direction generally perpendicular to the direction thatenergy is emitted from the transducer.
 16. The catheter of claim 1,further comprising an irrigation passage extending through at least aportion of the catheter body and having an open distal end near thetransducer to introduce fluid to contact tissue being ablated with thetransducer.
 17. The catheter of claim 16, wherein the irrigation passageextends through the tip electrode.